Research into a DC circuit breaker for immediately blocking a fault current when a fault current occurs in a DC line has been continuously conducted. In particular, a DC circuit breaker in a High Voltage DC (HVDC) system can block a power flow occurring in a large-scale power plant within a time of 5/1000 seconds by combining a very fast mechanism with electric power electronics.
Unlike an Alternating Current (AC) current, such a DC current flows as a constant current, and thus there is a disadvantage in that, when a load short-circuit fault occurs, a fault current does not become a zero current, and a DC circuit breaker must control the flow of the fault current using a high arc current, thus making it more difficult to block a DC fault current than to block an AC fault current.
In the conventional art, a DC circuit breaker for instantaneously reducing a fault current immediately before blocking using magnetic field switching is disclosed. This DC circuit breaker is problematic in that, in spite of various advantages of a DC current, such as low inductive disturbance, high circuit stability, and excellent transmission efficiency, it is impossible to sufficiently control an arc current, thus continuously permitting a DC fault current, and consequently leading to a large-scale fire accident.
In order to solve the above problem, conventional technology for applying an arc extinction device to a DC circuit breaker is presented. This is configured such that at least one pair of magnets is arranged with a switch interposed therebetween, and an arc current is blocked by increasing resistance to the arc current. However, a high-voltage DC circuit breaker is problematic in that an arc current depending on a high current is generated, so that the volume of magnets must be increased so as to increase resistance to the arc current and there is a limitation in increasing the size of a resistor, thus decreasing the speed at which the arc current is blocked.